feat: Create formatter module for Claude Code-style output

[mkusaka]

Overview

This issue is part of implementing Claude Code-style formatting (#171). We need to create a formatter module that handles different display formats (List, Preview, Detail) according to Claude Code's visual style.

Requirements

Formatter Types

1. List Formatter

   • Single-line display with newlines replaced by spaces
   • Tool executions as ToolName(args)
   • Long arguments truncated with …
   • Example: Bash(git commit -m "feat: enhance...")

2. Preview Formatter

   • Multi-line with Claude Code markers
   • First few lines followed by … +XX lines (ctrl+r to expand)
   • Format:

     ⏺ ToolName(arguments)
       ⎿ Result content
          More content
          … +XX lines (ctrl+r to expand)
     

3. Detail Formatter

   • Complete content without truncation
   • All markers and formatting preserved
   • No … +XX lines truncation

Implementation Details

Create new file: src/output/formatter.rs

use crate::schemas::tool_parser::{ParsedMessage, ToolExecution};

pub enum DisplayFormat {
    List,
    Preview { max_lines: usize },
    Detail,
}

pub struct ClaudeCodeFormatter {
    format: DisplayFormat,
}

impl ClaudeCodeFormatter {
    pub fn new(format: DisplayFormat) -> Self { }
    
    pub fn format_message(&self, parsed: &ParsedMessage) -> String { }
    
    pub fn format_tool_execution(&self, tool: &ToolExecution) -> String { }
    
    pub fn format_thinking_block(&self, content: &str) -> String { }
}

// Utility functions
pub fn truncate_with_ellipsis(text: &str, max_len: usize) -> String { }
pub fn format_line_count(count: usize) -> String { }
pub fn indent_content(content: &str, level: usize) -> String { }

Special Characters

• ⏺ (U+23FA) - Record button for actions
• ⎿ (U+23BF) - Circuit ground for results
• ✻ (U+273B) - Teardrop-spoked asterisk for thinking
• … (U+2026) - Horizontal ellipsis for truncation

Formatting Rules

1. Indentation: 2 spaces after ⎿
2. Line truncation:
   • List view: ~100 chars max
   • Preview: configurable (default 5 lines)
3. Argument truncation: Show first part + ... for long arguments

Testing

• Unit tests for each formatter type
• Tests for special character handling
• Tests for multi-byte character safety (Japanese, emojis)
• Edge cases (empty content, very long lines)

Acceptance Criteria

• List formatter produces single-line output
• Preview formatter shows truncated multi-line output
• Detail formatter preserves complete content
• Special Claude Code markers render correctly
• Handles multi-byte characters safely
• All tests pass
• Documentation with examples

Dependencies

• Depends on: feat: Implement tool execution parser for Claude Code formatting #193 (tool execution parser)
• Blocks: UI and CLI formatting issues

References

• Parent issue: feat: Add Claude Code-style output formatting to interactive UI and CLI #171
• Claude Code display patterns documented in feat: Add Claude Code-style output formatting to interactive UI and CLI #171